Liners are used in conjunction with protective headgear, such as helmets designed for use with various sports and other outdoor activities, primarily to be interposed generally between the interior surface of the headgear and a wearer's head. Most liners are configured for wearer comfort, but some may also or alternatively serve a protective function, such as by including cushions, pads, or other materials to soften or prevent the impact of the wearer's head against the interior of the headgear, such as when the headgear exterior is subject to an impact or other force.
Many head or brain injuries incurred while wearing protective headgear, however, are caused or exacerbated by what may be referred to as a “rebound effect”: in the event of a sudden force delivered to the headgear, the wearer's head will tend to initially lurch toward the point of impact and then recoil or rebound from the headgear interior (or cushioning system) away from the point of impact. In certain instances, it is the energy associated with the rebound effect, sometimes regardless of whether the initial impact is cushioned, that is primarily responsible for the severity of head injuries sustained while wearing headgear.
Headgear liners or protective systems that include a plurality of fluid-filled cushions or chambers may be found, for example, in U.S. Pat. No. 5,720,051, U.S. Pat. No. 4,566,137, U.S. Pat. No. 4,375,108, U.S. Pat. No. 4,370,754, U.S. Pat. No. 4,354,284, and U.S. Pat. No. 4,287,613. In some of these disclosures, the fluid-filled cushions are joined together to allow the flow of fluid from one cushion to an adjoining one, such as to absorb and/or distribute the energy from an impact to the headgear over a large area of the wearer's head. However, none address the rebound effect as explained above. Moreover, although the headgear with which some of these liners are used may employ a chinstrap or other device to orient the headgear on a wearer's head, none of the liners themselves include such a feature. The complete disclosures of the aforementioned publications are hereby incorporated by reference for all purposes.